1. Field of the Invention
The present invention relates to a drying device for an automatic developing apparatus.
2. Description of the Related Art
With advances in electronics, a rapid photographic process has been required in the field of silver halide photography. Particularly, a rapid process is required in processing some photosensitive materials such as sensitive material used for graphic arts, scanners and X-rays. The term "rapid process" as described herein means a process in which the amount of time from the time when an end of a photosensitive material is inserted into a photographic processor, i.e., an automatic developing apparatus, to the time when the end is removed from a drying area after the photosensitive material has passed through a processing area for developing, fixing and washing, and a drying area, is in a range of 20-60 seconds. In order to reduce this processing time, a velocity of the photosensitive material which is transported in the photographic processor is increased. However, only an increase of the conveying velocity results in inconveniences such as insufficient fixing and drying.
Accordingly, chemically effecting rapid process of the photosensitive material has been proposed. Such a process includes, for example, increasing the concentration of thiosulfate in a fixing liquid in order to accelerate a fixing velocity, or hardening the membrane of the photosensitive material in order to improve the drying characteristics of the photosensitive material.
However, although a hardening agent such as a water soluble aluminum compound must be included in a fixing liquid in order to fix the photosensitive material whose membrane is hardened, the hardening agent such as a water soluble aluminum compound works to decelerate the fixing speed. Therefore, if no hardening agent such as a water soluble aluminum compound is included at all in the fixing liquid, or if the amount of the hardening agent included therein is very small, a situation arises in which the drying characteristics of the photosensitive material may deteriorate because the swelling rate of an emulsion on the photosensitive material increases. Thus, few attempts to reduce the hardening agent such as a water soluble aluminum compound have been made since such a chemical approach for the rapid process has a deleterious effect on the fixing speed and the drying speed.
As a result, emphasis nowadays is put on accelerating the drying speed in a drying area of the automatic developing apparatus. These efforts have resulted in providing a hot-air blowing system and a hot-air blowing system with a far infrared radiant heater (Japanese Patent Application Laid-open No. 3-54560).
In the hot-air blowing system, a photosensitive material, after having had the water on its surface squeezed off in a squeezing portion of the automatic developing apparatus, is conveyed to a drying area. The surface of the photosensitive material is blown by hot air, thereby the photosensitive material is dried.
The photosensitive material to which this hot-air blowing system is applied has drying properties such that, as illustrated in FIG. 5(A), water content is evaporated from the surface of the photosensitive material at a constant rate by the supply of heat from hot-air blowing at an initial step of drying, while the surface temperature of the photosensitive material is constant. This condition is referred to as a constant-rate drying region A. Then, when the evaporation process is performed continuously after the constant-rate drying region A, water content is evaporated even from the emulsion layer of the photosensitive material which is referred to a decreasing-rate drying region B. In this region B, as the evaporation rate of water content becomes lower, the surface temperature of the photosensitive material rises higher. If excessive drying is rapidly performed by applying the excessively hot air to the photosensitive material, there exists the possibility of producing an area which is not suitably dried because only the surface of the photosensitive material is hardened even though a large amount of water remains inside of the emulsion layer of the photosensitive material, thereby causing a so-called drying mark. Accordingly, in order to sufficiently evaporate water from the inside of the emulsion layer in the decreasing-rate drying region B, it is necessary to maintain a fixed rate of change [(C2-C1)/T5] of the surface temperature (C) of the photosensitive material with respect to the drying time (T5). It is also necessary to restrict the quantity of heat in the hot air and to dry the photosensitive material in a predetermined time.
The surface temperature of the photosensitive material is shown as C1 in the constant-rate drying region A. After a predetermined period of time passes after the temperature rises up to C2 which is substantially the same temperature as that in the drying area, the photosensitive material is removed from the automatic developing apparatus. The point C2 to which the surface temperature in the photosensitive material rises, is referred to as drying point (D).
At the drying point (D), water content is evaporated to the extent that the treatment of the photosensitive material is of no problem, and the photosensitive material is dried to the extent that no uneven gloss occurs on the surface of the photosensitive material. Excessively drying the photosensitive material after the drying point (D) results in a difference in surface gloss of the emulsion layer of the overdried photosensitive material, thereby causing a drying mark.
Thus, in order to reduce the drying time (T) by taking the drying property of the photosensitive material into account, increasing the amount of heat in the constant-rate drying region A has been proposed. Correspondingly, as illustrated in FIG. 5(B), it has been suggested that the time during the constant-rate drying region A be reduced (T4&lt;T3) and the drying time (T) in the drying area be reduced using a hot-air blowing system with a far infrared radiant heater.
However, even in the above-described system, it is necessary to keep a fixed rate of change [(C2-C1)/T5] of the surface temperature (C) of the photosensitive material with respect to the drying time (T5) in the range of from the boundary area of the constant-rate drying region A and the decreasing-rate drying region B, to the drying point so that insufficient drying and the like does not occur. Therefore, the drying time (T5) in the decreasing-rate drying region B cannot be reduced, thereby limiting the reduction in the drying time (T) in the drying area.